policy: T5069: large-community-list regex validator should allow whitespace

* Re-introduce the whitespace/pattern matches ' ' and '_' as allowed
* Perform a general Python regex validity check (not 100% 1003.2, but in combination
  with allowedChars, pretty close)
* Introduce a warning against potentially malformed or over-complex patterns,
  but leave it up to the user to resolve - there are plenty of useful
  expressions we cannot validate easily

2 files changed, 31 insertions, 6 deletions

diff --git a/src/conf_mode/policy.py b/src/conf_mode/policy.py
index a90e33e81..ec9005890 100755
--- a/src/conf_mode/policy.py
+++ b/src/conf_mode/policy.py
@@ -14,6 +14,7 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
+import re
 from sys import exit
 
 from vyos.config import Config
@@ -24,9 +25,20 @@ from vyos.frrender import get_frrender_dict
 from vyos.utils.dict import dict_search
 from vyos.utils.process import is_systemd_service_running
 from vyos import ConfigError
+from vyos.base import Warning
 from vyos import airbag
 airbag.enable()
 
+# Sanity checks for large-community-list regex:
+# * Require complete 3-tuples, no blank members. Catch missed & doubled colons. 
+# * Permit appropriate community separators (whitespace, underscore)
+# * Permit common regex between tuples while requiring at least one separator
+#   (eg, "1:1:1_.*_4:4:4", matching "1:1:1 4:4:4" and "1:1:1 2:2:2 4:4:4",
+#        but not "1:1:13 24:4:4")
+# Best practice: stick with basic patterns, mind your wildcards and whitespace.
+# Regex that doesn't match this pattern will be allowed with a warning. 
+large_community_regex_pattern = r'([^: _]+):([^: _]+):([^: _]+)([ _]([^:]+):([^: _]+):([^: _]+))*'
+
 def community_action_compatibility(actions: dict) -> bool:
     """
     Check compatibility of values in community and large community sections
@@ -147,6 +159,10 @@ def verify(config_dict):
                     if 'regex' not in rule_config:
                         raise ConfigError(f'A regex {mandatory_error}')
 
+                if policy_type == 'large_community_list':
+                    if not re.fullmatch(large_community_regex_pattern, rule_config['regex']):
+                        Warning(f'"policy large-community-list {instance} rule {rule} regex" does not follow expected form and may not match as expected.')
+
                 if policy_type in ['prefix_list', 'prefix_list6']:
                     if 'prefix' not in rule_config:
                         raise ConfigError(f'A prefix {mandatory_error}')
diff --git a/src/validators/bgp-large-community-list b/src/validators/bgp-large-community-list
index 9ba5b27eb..75276630c 100755
--- a/src/validators/bgp-large-community-list
+++ b/src/validators/bgp-large-community-list
@@ -1,6 +1,6 @@
 #!/usr/bin/env python3
 #
-# Copyright (C) 2021-2023 VyOS maintainers and contributors
+# Copyright (C) 2021-2025 VyOS maintainers and contributors
 #
 # This program is free software; you can redistribute it and/or modify
 # it under the terms of the GNU General Public License version 2 or later as
@@ -17,18 +17,27 @@
 import re
 import sys
 
-pattern = '(.*):(.*):(.*)'
-allowedChars = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '.', '+', '*', '?', '^', '$', '(', ')', '[', ']', '{', '}', '|', '\\', ':', '-' }
+allowedChars = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '.', '+', '*', '?', '^', '$', '(', ')', '[', ']', '{', '}', '|', '\\', ':', '-', '_', ' ' }
 
 if __name__ == '__main__':
     if len(sys.argv) != 2:
         sys.exit(1)
 
-    value = sys.argv[1].split(':')
-    if not len(value) == 3:
+    value = sys.argv[1]
+
+    # Require at least one well-formed large-community tuple in the pattern. 
+    tmp = value.split(':')
+    if len(tmp) < 3:
+        sys.exit(1)
+
+    # Simple guard against invalid community & 1003.2 pattern chars
+    if not set(value).issubset(allowedChars):
         sys.exit(1)
 
-    if not (re.match(pattern, sys.argv[1]) and set(sys.argv[1]).issubset(allowedChars)):
+    # Don't feed FRR badly formed regex
+    try:
+        re.compile(value)
+    except re.error:
         sys.exit(1)
 
     sys.exit(0)